Call transmitter



001.2 1 945. L MEAgHAM 2,386,133

CALL TRANSMITTER Fiied Dec. 9, 1943 Patented Oct. 2, 1945 NITED STATES; ersurr OFFICE; I

can. TRANSMITTER Earned A. Meaehanr, Summit, N. J., assignor to- Bell TelephoneLaboratories, Incorporated, New York, Y., a corporation of New York epplicatitnpeeemter 9 ,1943, Serial No. 513,559 eel-ai s; ((31.179-90) This invention relates to. call' transmitters and;

more particularly; to key-control! transmitters which are adapted" to generate alternating cure rent key signaling impulses that. may. be :utilized;

in one specific use, to indicate telephone station designations...

At the present. time. telephone. systems which operate on the basisof keyed alternating. current signals are systems inwhich. the-signals them selves, when indicating awanted. telephonenumeher; are impulseslcomprising: coded combinationsof frequencies. preferably within: the voice? f-re-- quency range. and these. impulsesare produced.

either by an alternating current generator hay inga number ofireeds which can be simultaneously plucked in the. required. combina'ti0nvbya--- digit designating key to, induce the.-wanted=frequencies inaa.pickeupxcoil interlinked witha'magenetic field, or by the permutative application: to.

the line of the required number of generators each individual, to. one of the. frequencies. At the remote end. of the line these frequenciesare. received by suitable. frequency-responding appae ratus which, inthemost. general case, comprises. achannelfor each frequency thatincludesv-a: fi1-' ter networktunedto the. frequency to-berpassedg an amplifier, a rectifier for changing-theamplia fied. frequency into a; direct current anda senssitive relay to'operate in. response to that: cur

rent, the. momentary operation. of the latter usually being. registered. intasuitablel storage device of a switching. control. mechanism called, the

sender which, in response to the registration,

controls the selectivepositioning of the switches that are to connect withthewantedliner Telephone systems. operating on: alternating current impulses have. a. number of. advantages; over thosewhich operate: Qndirect current im-' pulses; ing" range and are faster than the dial. operated systembecause the. closure. period. of,- therequirednumber ofkeys, each. practically of equaldura- For example,.they permit allonger diale ordinarily necessary for response to the-incoming. signal frequencies; for instance;. if economies could be. eifected in;the channelstwhichlrespondr vto the individual frequencies; As already intimated, these channels are fairly. expensive. dueto the necessity of providing for each channel; a complex filter network, an amplifier, a'rectie fier and. a. sensitive relay and, further; additional? equipment to protect. the channels against false.

response to noise induced. currents. t 1

To the end of simplifying thequantityotcen tral ofiice equipment necessary for key pulsing;

and thus provide more'efiicient telephone: service.

I I have. devised-atelephone system covered by copending application serial No. 514,482, filed Nov. 16, 19453, which operates 011:. polarized? signals; that is, a. telephone system: in: which the designationv of the wanted line consistsentirely of acodedsuccession: of spaced. positiveandnegfl In other words, theiimpulsesi ative wave-fronts; that comprise the wanted designation: do not consist of a train; of} alternations: ofi mixed or:

single frequencies? persisting onthe: line for a;

given-period; but only" of; a number oi? single hztlfs cycles p'ermutatively 'spacedalongi thewave traihl" to denote the coded indication ot' a digit. or char-- acter.

The present'invention has to do with: acallf transmitter intended for use with the invention- 1 covered by the above-mentioned copending application or, for that-matter, with any other in vention or device in which polarized impulses areutilized, and the object ofthepresent inventien is a call transmitter capable ofgeneratingi polarized impulses of the typedescribedwhich is simple and reliable to operate, compactin struc ture and economical to produce.

More specifically, the invention, in one embodiment described herein by way of illustration,

comprises an electr.omechanicaldevice provided with a number of numerical keys thedepression I of any one of which causes-a number of preten sioned magnetic reeds housed within a coilieacli to traverse an appropriately poled magnetic field. in a sequence which is'determined by' a permutation. code.

As a med moves across a field, it effects. a momentary change in. the lines of .force' that traverse the coil and thereby' causes a pulse to be induced in the coil the polarity of which I is determined by the direction .of' the magnetic field in which the reed has moved; On the release of .the key, the reeds are slowly restored to their pretensioned position so as, to avoid. any rapid change of flux through the coil and therefore avoid the production of any detectable pulses on the return of the key.

Other features and advantages of the invention will appear from the following description and the claims appended thereto, reference being had to the accompanying drawing in which:

Fig. 1 shows a plan view of the keys and bars of the device of my invention as incorporated in a typical telephone subscribersset Fig. 2 is a plan view of the device itself;

Fig. 3 is a front view of said device; While Fig. 4 is a typical wave which may be produced by the device.

Fig. 5 is a partial isometric showing of the rebered key members Kl, K2, K3, K4, K5, K's, Kl,

K8, K9 and Kl!) are pivotally supported on a shaft 25 which is rotatively mounted at both ends in the upright supports 23 secured to the base 20, which also secures the L-shaped plate 2?. A

plurality of U-shaped bars BI, B2, B3, B4 and r B5 are freely supported on shaft 25 and are disposed for sequential operation by the downward movement of. any one of the keys lib-K5 in combinations'of four in accordance with a number code. To secure the sequential operations of the different bars Bl-B5 as shown more particularly in Fig. 5, said bars are individually notched to different depths directly underneath the shank of the different key members in accordance with the sequence in which they are to be operated, the bar to be operated first in a sequence, for example, having a notch of minimum depth to insure first engagement by the shank of the key, the bar to be operated fourth in said sequence having a proportionally deeper notch, while the bar which is not to be engaged has a notch of a depth to insure that when the key is fully depressed, its shank willfully penetrate the notch without moving the bar.

To the adjacently disposed pivoted arms of the bars BIB5 are secured the lever members Ll, L2, L3, Ld'and L5, respectively, each lever mem-' ber being provided with an inner finger 30 and an outer finger 36, as shown in Fig. '3. Each lever member is also provided with an apertured lug 28 to which is attached one'end of an individual spring 26, theother end of said spring being made secure in a hole in the upright plate 21, identical springs being provided for each lever member as shown. The spring 26 pulls on the lug 28, and since a bar Bsecured to a lever Lis pivoted on the shaft 25, the spring tends to move both the bar and the connected lever in a clockwise direction and cause the finger 36 of the lever nor-- from the key member, the tension stored in spring 26 hooked to the lever of said bar will cause the lever and the bar to be rotated clockwise, the cross-member of the bar lifting the key K-- back to its normal position by the time the lug 36 has pushed the reed R back to its own normal position as explained hereinafter.

On the base 20 is mounted an alternating current generator comprising two permanent horseshoe type magnets 40 and MY within which is secured the common coil 42. Each of the two magnets is made of two parts, one slightly longer than the other, and both magnets are mounted in opposite senses upon the base 26, that is, ma net 4!), the forward magnet, is mounted so that its north pole N is on top while magnet ilY is r so mounted that its south pole S is on top. As

- reeds are resting against.

shown in Fig. 3, thenorth pole N of the forward magnet 40 is longer than and overhangs the south pole S, while the south pole S of the rear magnet MN is longer than and overhangs its associated north pole N. Clamped between the poles of each .within the magnets that, unrestrained, their curvature will cause them to assume a downward position with their respective forward ends resting upon the lower poleof the magnet. Now the magnets 40 andABY are so mounted upon the base 20 in relation to the lever members Ll-LE that when said lever members are in the normal position, their respective fingers 36 will push the reeds R up against the upper poles of the magnets, thereby placing said reeds under tension, the length of the reeds being such that the outer ends thereof protrude slightly beyond the edge of the upper pole. s

A tripping device supported on a shaft BL secured between the clips 2 and 3 is located between the inner and outer fingers 3B and 35 of the levers LIL5. This device consists of five Y-shaped tripping members pivotally supported on the shaft BL and are so spaced upon said shaft that each is in aligned relation with a reed R and the finger 36 of an associated lever member L. 7 A spring 6, individual to each tripping member A, is coiled around the shaft BL with one end resting on the curved underside of the lower pole of the magnet and the other end against the right under surface of the associated,

tripping member 4, the coiling of the spring around the shaft BL being such as to impart counter-clockwise rotation to its associated tripping member. Thus if any force is applied to the right end of a tripping member 4 to turn the latter clockwise, tension is stored in the spring which later will be utilized to turn the tripper 4 back to its original position. Again, if anykey member K is depressed and the shank thereof engages a bar B to cause the attached lever member L to be pushed downward, the finger 36 of the lever member is drawn away from the reed R,.leaving the latter to be supported against the upper pole of the magnet solely by the left end of the associated tripper 4. As the lever L continues its downward motion, the inner finger 30 engages the right end of the tripper and the force applied to the tripper by the lever member causes the left end of the tripper to slip out from under the reed R which, being now freed from all restraints, rapidly moves across the gap between the two poles of the magnet to come to rest upon"- theface of the" lower pole". When the reed strikes the face of the lower: pole, it wi1l, .of

course vibrate slightly; but with. proper design-of the reed: this vibration willbe of short duration and; of; insufiicient: amplitude to affect the; state ofmagnetic-saturation of the reed. i

Having described the diiferent mechanical elements oi the device. together with their arrangement and: interrelatiom I: will now describe the manner in which the device operates.

With all: therce-ds positioned against the upper. pole of their respective. magnets, the lines. of torce" of: the magnet .will have a path of lowest reluctancethrough thereeds, the direction of these lines beingdetermined; ofcourse; by the. pole against which the reeds areheld by thefingers 36a. Thus, if we consider the three reedsclampedbetweenthe poles-of the. forward magnet 49; the lines will flow into the reeds. at the forward ends and backv into the upper part of the magnet at. the rear end since the magnet 4E5. is formed with;

its north-poleN ontop and the south pole S- below. On the other hand, for the two reeds clamped between the polesof the rear magnet:

MY, the lines of force will be oppositely directed, entering the reeds from the upper element of the magnet at the-rear end thereof andleaving the reedsat theforward end thereof to: flow back into said upper element of the magnet. Since the coil 42. is enclosedzwithin both magnets, the

fields of thetwo magnets interlink the coil.

Now when a key K is depressed, four-oh the five bars Bl-B5. are sequentially'engaged' by the shank of the key in accordance withzthedepth of their respective notchings. As each bar'issene gaged, it is forced down against the tension of.

its restoringspring 26. until-the key comstothe end of its stroke As the bar moves down, however, the outerfinger 3.5.of the lever member L- connected to the engaged bar 3- i withdrawn from the bottom of a reed R, and when the lever member has moved to a depth at which its inner finger engages the right end of the tripper 4, the reed R is released and, due to its downward curvature, snaps from engagementwlth the upper pole of the magnet into engagement with the lower pole without appreciable vibration,

Considering more particularly the front reed clamped within the magnet Ml, as the forward end of the reed leaves the north pole N and an air gap is introduced between the pole and the reed, the reluctance of the magnetic circuit increases and the resulting flux decreases, said flux continuing to decrease at approximately the same rate until the reed is midway between the two poles at which time its valu will pass through zero and reverse in direction. Since the flux interlinks the coil 42, an electric potential will be induced therein whose direction and intensity are respectively determined by the direction and magnitude of the time rate at which the flux changes. As the forward end of the reed approaohes the south pole of the lower magnet and the gap between this pole and the reed is reduced, the reluctance between the reed and the lower magnet is progressively decreased, the flux due to this magnet rapidly increases in the reed, reaching saturation when the reed comes to rest upon the surface of the pole. Since the flux due to the lower magnet is opposite in direction to that due to the upper pole, and since this flux likewise interlinks the coil 42, the increase of this flux induces an electric potential in the coil which is in the same direction as that produced by the decrease of the flux of the upper magnet and. is

equally proponti'onalitorthe time'rates at;.which.-the: flux is caused to be increased. .Thusgdependinga upon"; whether the reed: is located. between the twoipolegof mEgllEtiQWOI'JthEtWO oppositely disposed poles of: magnet. Y, a. continuous pulseis': producedLin: the: coil. which, starting: from zero.- Value; reaches amaximumr amplitude in. the di.- rection. determined: by the flux: Ofi the upper pole; and-ithen'i declines again'to zero, as the; reed, ap"- proaching. the. surface :of the lower pole, becomes; saturated; If. the reed; shouldvibrate slightly, onistriking; the: lower pole, the generation. theretby: of unwanted. electricaltransienisis precluded; by the saturation of thereedu Each of thereedss released at spacediintervalsiby thenotchings, on the bars: engaged? sequentially by the; operatedi key member K.,. produces a similar pulse; thepolarity, of which. is. determined. by whether the:

reed which: is released is (clamped within magnet;

r lll'onwithin; magnetd fhx A series: offounsuchpulses produced. by the; depressionrof akey K.-

is indicatedin'Fig. 4. it 7 l i When-.the-keyK--is released; the-tensionstored:

inthe-springs 25: Of thefour operated bars B.- wille urge saidzbarsi to? rotate in a clockwisev direction:

' by means of its outward finger 36 pushing its,

willrbexgenerated: 011i thereturn. of. the keyivflher inner finger 311 does not disengage the tripper 4:

aligned reed=Ragainst the upper pole-ofthe magnet. Because ofithisislow restoration 0t thereed back. to its original" position, no detectable: pulse;

until; the finger. 3.6: has; come. toirest against. thereedaw-herr the: latter. abutsgthe: underside of the upper pole. Since the spring 6 was placed under tension by the downward stroke of the lever, the disengagement of the lever from the tripper 4 will cause the spring to turn counter-clockwise until the left end of the tripper is lodged underneath the restored reed. The same restoringaction, of course, takes place with each reed released for operation.

While I have described my invention in connection with a specific embodiment thereof, it is to be understood that various other embodiments thereof may be made by those skilled in the art Without departing from the spirit of the invention as defined within the scope of the appended claims.

What is claimed is:

1. A telephone call transmitter comprising a plurality of reed elements, a plurality of means holding said elements in pretensioned positions, and a set of key members each corresponding to a digit to be transmitted for actuating said means permutatively in a sequential order for releasing said elements from their pretensioned positions in the same order.

2. A telephone call transmitter comprising a plurality of magnetic reeds, a set of key members each corresponding to a digit or characten'a plurality of bars disposed underneath said key members and notched at varying depths for actuation by each of said key members permutatively in a sequential order, lever members carried by the bars having means for holding the reeds normally in a pretensioned position, and a plurality of means for holding said reeds in said pretensioned positions following a partial operation of the bars by a, key member and for disengaging said means from the reeds upon the full operation of said key member. 7

3. A mechanism for the production of a series of single cycle pulses comprising a plurality of oppositely disposed magnets, a coilinterlinked with the flux of said magnets, a plurality of magnetic reeds formed with an initial curvature and clamped within said magnets, means for normally and severally holding said reeds in a pretensioned condition against opposite poles of said magnets, and means for releasing said reeds in a permutative sequential order whereby their respective movements across the pole gap each induces an impulse of potential in said coil.

4. A mechanism for the production of a series of single cycle pulses comprising a plurality of oppositely disposed magnets, a coil interlinked with the magnetic field of said magnets, a plurality of magnetic reeds clamped between the poles of said magnets, each of said reeds having acurvature such that,-in its clamped position, one end thereof will rest against a pole of a magnet, an actuating member for each of said reeds, means for causing each of said actuating members normally to pretension its associated reed against the opposite pole of the magnet, and a set of manually operable keys for engaging said actuating membars in a permutative sequential order for releasing the associated reeds in the same order, where'- by each of the released reeds moves across the pole gap and induces an impulse of potential in said coil.

'5. A call transmitter comprising two magnets disposed in opposite polar relation, a coil interlinking the magnetic field of both of said magnets,

tial order individual to each one of said key members, said means normally engaging said reeds for severally moving them to a pretensioned position against opposite poles of said magnets, a tripping member for each for holding the reed in said pretensioned position and operated by one a of said means to release the reed from its pretensioned position following the operation of one of said keys, whereby the movement of the reed across the pole gap following its release will induce an impulse of potential in said coil.

a 6. A device for generating a train of single cycle pulses, the polarity of any pulse in the train hearing either the same or the opposite relation to the polarity of any other pulse, comprising a plurality of oppositely disposed magnets, a coil mounted within said magnets to interlink the magnetic fields thereof, curved magnetic springs clamped between said magnets and surrounded by said coil, a device for each spring normally holding said spring pretensioned against that pole of a magnet which is remote from the curved end of the spring, whereby a portion of the magnetic flux emanating from the pole in contact with the spring traverses and saturates the spring, and keying means for operating said devices in a predetermined sequence whereby the springs are released sequentially from their pretensioned positions to assume their respective normally curved positions, and whereby during the movement of each of the springs through the pole gap the magnetic flux through the spring is changed from a maximum in one direction to a maximum in the opposite direction to induce a single cycle pulse in said coil, the polarity of said induced pulse being determined by the disposition of the two poles of the magnet within which the spring is clamped. V V

" LARNED A. MEACHAM. 

